1. Field of the Invention
The present invention relates to a method for predicting a modal damping ratio of a composite head.
2. Description of the Related Art
A composite head has been known as a head including a plurality of materials. The compositing of the head advantageously enhances a degree of freedom of design. Particularly, a large-sized hollow head has a low degree of freedom of wall thickness distribution. For example, it is difficult to provide a center of gravity in a lower position in the large-sized hollow head. The composite head can solve the problem. The composite head is effective to provide the center of gravity in the lower position in the large-sized hollow head, for example.
The typical example of the compositing is combination use of a titanium alloy and a material having specific gravity lighter than that of the titanium alloy. Examples of the material having specific gravity lighter than that of the titanium alloy include CFRP and a magnesium alloy. The CFRP means carbon fiber reinforced plastic.
The use of the material having lighter specific gravity can create an excess weight. The excess weight can be disposed at a desired position. The excess weight can be utilized for design of a position of a center of gravity. Furthermore, the position of the center of gravity can be moved depending on where the material having lighter specific gravity is disposed. An example of a constitution effectively providing the center of gravity in the lower position is a head having a crown made of CFRP and a sole and a face made of a titanium alloy.
On the other hand, the composite head may bring about a short-time ball hitting sound. For example, the CFRP causes large vibrational energy loss. Therefore, the composite head including the CFRP brings about a short-time ball hitting sound. The short-time ball hitting sound tends to be undesirable for golf players. It is difficult to improve the ball hitting sound in the composite head.
A large-sized hollow head sold in these days brings about a loud ball hitting sound. Therefore, the golf players recognize the ball hitting sound as one of evaluation items of a golf club. A comfortable ball hitting sound is important for the golf players.
One of methods improving the ball hitting sound is to repeat a trial production and evaluation. However, when the ball hitting sound can be predicted by simulation, the trial production is unnecessary, to efficiently improve the ball hitting sound.
Japanese Patent Application Laid-Open No. 2006-23955 discloses a ball hitting sound prediction method. In the prediction method, a modal parameter calculated by eigenvalue analysis is used. In the gazette, a damping value obtained by experimental modal analysis is used as a mode damping value. In this case, the damping value cannot be obtained as long as a real head does not exist. Then, the experimental modal analysis is conducted using a real head having substantially the same volume as that of a calculation model, to acquire the average value of the damping values in each natural frequency up to 10 kHz.